U.S. patent number 6,897,183 [Application Number 10/375,744] was granted by the patent office on 2005-05-24 for process for making image recording element comprising an antistat tie layer under the image-receiving layer.
This patent grant is currently assigned to Eastman Kodak Company. Invention is credited to Eric E. Arrington, Thomas M. Laney.
United States Patent |
6,897,183 |
Arrington , et al. |
May 24, 2005 |
**Please see images for:
( Certificate of Correction ) ** |
Process for making image recording element comprising an antistat
tie layer under the image-receiving layer
Abstract
This invention relates to a process for making an
image-recording element, for example a dye-receiving element for
thermal dye transfer, that includes a support having on one side
thereof a image-receiving layer and, between the image-receiving
layer and the support, a tie layer comprising a thermoplastic
antistat polymer. In one embodiment, the process comprises (a)
forming a first melt of a polymer for the surface layer and a
second melt comprising a thermoplastic antistat polymer in a
polymeric binder; (b) coextruding the two melts onto a polyolefin
support; (c) stretching the coextruded layers to reduce the
thickness; and (d) applying the coextruded melts to a support while
simultaneously reducing the temperature below the Tg of the
composition of the surface layer.
Inventors: |
Arrington; Eric E.
(Canandaigua, NY), Laney; Thomas M. (Spencerport, NY) |
Assignee: |
Eastman Kodak Company
(Rochester, NY)
|
Family
ID: |
32771470 |
Appl.
No.: |
10/375,744 |
Filed: |
February 26, 2003 |
Current U.S.
Class: |
503/227;
264/173.16; 264/177.19; 427/152; 264/211.2 |
Current CPC
Class: |
B41M
5/52 (20130101); B32B 27/28 (20130101); G03G
7/008 (20130101); B32B 27/08 (20130101); B29C
48/08 (20190201); G03G 7/0046 (20130101); B32B
38/0012 (20130101); B29C 48/307 (20190201); B41M
5/42 (20130101); B29C 48/21 (20190201); B29C
48/04 (20190201); B32B 2038/0028 (20130101); B32B
2307/75 (20130101); B29C 48/84 (20190201); B41M
2205/32 (20130101); B41M 5/5272 (20130101); B29C
48/05 (20190201); B41M 2205/02 (20130101); B29C
48/85 (20190201); B32B 2307/21 (20130101); B29C
48/83 (20190201); B32B 37/153 (20130101) |
Current International
Class: |
B41M
5/50 (20060101); B41M 5/40 (20060101); B41M
5/42 (20060101); B41M 5/52 (20060101); B41M
5/00 (20060101); B41M 005/035 (); B41M
005/38 () |
Field of
Search: |
;264/173.16,177.19,211.2
;427/152 ;503/227 ;428/195.1,32.39,32.51 ;364/173.16,177.19 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hess; Bruce
Attorney, Agent or Firm: Manne; Kathleen Neuner
Claims
What is claimed is:
1. A process of forming a multilayer film comprising at least two
layers, a surface layer and a tie layer directly adjacent the
surface layer, wherein the process comprises: (a) forming a first
melt, for the surface layer, comprising a first polymeric binder;
(b) forming a second melt, for the tie layer, comprising a
thermoplastic antistat polymer, wherein the second melt exhibits a
viscosity that is not more than 10 times or less than 1/10 that of
the first melt during the following extrusion step; (c) coextruding
the two melts to form a composite film; (d) stretching the
composite film to reduce its thickness; and (e) applying the
stretched composite film to a support while simultaneously reducing
the temperature of the composite film below the Tg of the surface
layer.
2. The process of claim 1 wherein the antistat polymer exhibits a
surface resistivity of 10.sup.5 to 10.sup.13 Ohms per square.
3. The process of claim 1 wherein antistat polymer is selected from
the group consisting of polyether-block copolyamides,
polyetheresteramides, segmented polyether urethanes, and
polyether-block-polyolefins.
4. The process of claim 1 wherein the composition of the tie layer
exhibits a viscosity in the range of is 100 to 10,000 poise at 1
sec.sup.-1 shear rate at a temperature between 100 and 300.degree.
C.
5. The process of claim 1 wherein the antistat polymer is a block
polymer which has a structure in which blocks of a polyolefin and
blocks of a hydrophilic polymer are bonded together alternately and
repeatedly.
6. The process of claim 5 wherein the blocks of the hydrophilic
polymer are polyether blocks.
7. The process of claim 6 wherein the polyether blocks are formed
from one or more alkylene oxides having 2 to 4 carbon atoms.
8. The process of claim 7 wherein the polyether blocks comprise
ethylene oxide, propylene oxide, butylene oxide, or combinations
thereof.
9. The process of claim 5 wherein the polyolefins is obtained by
polymerization of one or a mixture of two or more olefins,
containing 2 to 12 carbon atoms.
10. The process of claim 5 wherein the polyolefin of the block
polymer comprises carbonyl groups at both polymer termini and/or a
carbonyl group at one polymer terminus.
11. The process of claim 1 wherein the antistat polymer comprises a
block copolymer formed by the reaction of a mixture comprising a
modified polyether and a modified polyolefin.
12. The process of claim 1 wherein the anti stat polymer comprises
a block copolymer of polyethylene oxide polyether segments with
polypropylene and/or polyethylene polyolefin segments.
13. The process of claim 12 wherein a compatibilizer is
substantially absent from the tie layer.
14. The process of claim 12 wherein the block copolymer has a
number average molecular weight of 2,000 to 60,000 as determined by
gel permeation chromatography.
15. The process of claim 1 wherein the tie layer comprises an
antistat polymer in combination with a compatibilizer.
16. The process of claim 15 wherein the antistat tie layer is a
copolymer of polyether and polyamide.
17. The process of claim 1 wherein the thickness of the surface
layer is between 1 and 5 micrometers.
18. The process of claim 1 wherein the support is a multilayer
sheet or web.
19. The process of claim 18 wherein the support comprises a
compliant substrate sheet over a base support comprising a
polyolefin-containing surface layer.
20. The process of claim 19 wherein a surface of the support is a
polyolefin-containing film.
21. The process of claim 19 wherein the support further comprises a
backing layer on the base support.
22. The process of claim 19 wherein the surface layer is an imaging
layer for receiving an electrophotographic toner.
23. The process of claim 1, wherein the surface layer is an
image-receiving layer for receiving an image by thermal dye
transfer.
24. The process of claim 1, wherein the surface layer is a
dye-receiving layer, a pigment-receiving layer, or a
toner-receiving layer.
25. A process of making an image recording element comprising a
support having thereon an image-receiving layer and, between the
support and the image-receiving layer, a tie layer, wherein the
process comprises: (a) forming a first melt, for the
image-receiving layer, comprising a first polymeric binder; (b)
forming a second melt, for the tie layer, comprising a
thermoplastic antistat polymer, wherein the second melt exhibits a
viscosity that is not more than 10 times or less than 1/10 that of
the first melt when coextruded with the first melt; (c) coextruding
the two melts to form a composite film; (d) stretching the
composite film to reduce the thickness; and (e) applying the
stretched composite film to a support for the image recording
element while simultaneously reducing the temperature below the Tg
of the image-receiving layer.
26. The process of claim 25 wherein a surface of the support in
contact with the tie layer comprises a polyolefin.
27. The process of claim 25 wherein the support is a moving web and
the film extruded over the moving web.
28. The process of claim 25 wherein the image-receiving layer
comprises a polyester binder.
29. The process of claim 28 wherein the polyester comprises
recurring dibasic acid derived units and polyol derived units, at
least 50 mole % of the dibasic acid derived units comprising
dicarboxylic acid derived units containing an alicyclic ring within
two carbon atoms of each carboxyl group of the corresponding
dicarboxylic acid, and at least 30 mole % of the polyol derived
units containing an aromatic ring not immediately adjacent to each
hydroxyl group of the corresponding polyol, 25 to 75 mole % of the
polyol derived units of the polyester are non-aromatic and comprise
2 to 10 carbon atoms, and at least 0.1 mole percent, in sum total,
of (a) units, if any, derived from a multifunctional polyol having
more than two hydroxy groups, based on the total polyol component
in the polymer and (b) units, if any, derived from a polyacid
having more than two carboxylic acid groups, including derivatives
thereof, based on the total acid derived units.
30. The process of claim 28 wherein the average weight molecular
weight of the polyester is at least 50,000.
31. The process of claim 28 wherein the average weight molecular
weight of the polyester is 100,000 to 1,000,000.
32. The process of claim 28 wherein the polyester has a glass
transition temperature greater than about 40.degree. C.
33. The process of claim 28 wherein the polyester has a glass
transition temperature between 40.degree. C. and 100.degree. C.
34. The process of claim 28 wherein the polyester is blended with a
second polymer that is not a polyester.
35. The process of claim 34 wherein the second polymer is a
polycarbonate.
36. The process of claim 35 wherein the polycarbonate is a
bisphenol-A polycarbonate and the polycarbonate and polyester
polymers are blended at a weight ratio of from 90:10 to 10:90.
37. The process of claim 25 wherein the image recording element is
an electrophotographic recording element and the image-receiving
layer is a toner-receiving layer.
38. The process of claim 25 wherein the image recording element is
a dye-receiver element for thermal dye transfer and the
image-receiving layer is a dye-receiving layer.
39. The process of claim 25, further comprising an effective amount
of a release agent in the first melt.
40. The process of claim 25 wherein the image-receiving layer is a
dye-receiving layer, a pigment-receiving layer, and/or
toner-receiving layer.
41. The process of claim 25 wherein the image-receiving layer is 1
to 50 micrometers thick.
42. A process of forming a dye transfer image comprising: making an
image recording element comprising a support having thereon an
image-receiving layer and, between the support and the
image-receiving layer, a tie layer, by forming a first melt, for
the image-receiving layer, comprising a first polymeric binder;
forming a second melt, for the tie layer, comprising a
thermoplastic antistat polymer, wherein the second melt exhibits a
viscosity that is not more than 10 times or less than 1/10 that of
the first melt when coextruded with the first melt; coextruding the
two melts to form a composite film; stretching the composite film
to reduce the thickness; and applying the stretched composite film
to the support for the image recording element while simultaneously
reducing the temperature below the Tg of the image-receiving layer;
imagewise-heating a dye-donor element comprising a support having
thereon a dye layer and transferring a dye image from the dye layer
to the image recording element to form said dye transfer image.
Description
FIELD OF THE INVENTION
This invention relates to image recording elements, including
dye-receiving elements used in thermal dye transfer, and more
particularly to polymeric image-receiving layers for such
elements.
BACKGROUND OF THE INVENTION
In recent years, thermal transfer systems have been developed to
obtain prints from pictures which have been generated from a camera
or scanning device. According to one way of obtaining such prints,
an electronic picture is first subjected to color separation by
color filters. The respective color-separated images are then
converted into electrical signals. These signals are then operated
on to produce cyan, magenta and yellow electrical signals. These
signals are then transmitted to a thermal printer. To obtain the
print, a cyan, magenta or yellow dye-donor element is placed
face-to-face with a dye-receiving element. The two are then
inserted between a thermal printing head and a platen roller. A
line-type thermal printing head is used to apply heat from the back
of the dye-donor sheet. The thermal printing head has many heating
elements and is heated up sequentially in response to one of the
cyan, magenta or yellow signals. The process is then repeated for
the other two colors. A color hard copy is thus obtained which
corresponds to the original picture viewed on a screen.
Dye receiving elements used in thermal dye transfer generally
include a support (transparent or reflective) bearing on one side
thereof a dye image-receiving layer, and optionally additional
layers. The dye image-receiving layer conventionally comprises a
polymeric material chosen from a wide assortment of compositions
for its compatibility and receptivity for the dyes to be
transferred from the dye donor element. Dye must migrate rapidly in
the layer during the dye transfer step and become immobile and
stable in the viewing environment. Care must be taken to provide a
receiving layer which does not stick to the hot donor as the dye
moves from the surface of the receiving layer and into the bulk of
the receiver. An overcoat layer can be used to improve the
performance of the receiver by specifically addressing these latter
problems. An additional step, referred to as fusing, may be used to
drive the dye deeper into the receiver.
In sum, the receiving layer must act as a medium for dye diffusion
at elevated temperatures, yet the transferred image dye must not be
allowed to migrate from the final print. Retransfer is potentially
observed when another surface comes into contact with a final
print. Such surfaces may include paper, plastics, binders, backside
of (stacked) prints, and some album materials.
Polycarbonates (the term "polycarbonate" as used herein means a
polyester of carbonic acid and a diol or diphenol) and polyesters
have both been used in image-receiving layers. For example,
polycarbonates have been found to be desirable image-receiving
layer polymers because of their effective dye compatibility and
receptivity. As set forth in U.S. Pat. No. 4,695,286, bisphenol-A
polycarbonates of number average molecular weights of at least
about 25,000 have been found to be especially desirable in that
they also minimize surface deformation which may occur during
thermal printing. These polycarbonates, however, do not always
achieve dye transfer densities as high as may be desired, and their
stability to light fading may be inadequate. U.S. Pat. No.
4,927,803 discloses that modified bisphenol-A polycarbonates
obtained by co-polymerizing bisphenol-A units with linear aliphatic
diols may provide increased stability to light fading compared to
ummodified polycarbonates. Such modified polycarbonates, however,
are relatively expensive to manufacture compared to the readily
available bisphenol-A polycarbonates, and they are generally made
in solution from hazardous materials (e.g. phosgene and
chloroformates) and isolated by precipitation into another solvent.
The recovery and disposal of solvents coupled with the dangers of
handling phosgene make the preparation of specialty polycarbonates
a high cost operation.
Polyesters, on the other hand, can be readily synthesized and
processed by melt condensation using no solvents and relatively
innocuous chemical starting materials. Polyesters formed from
aromatic diesters (such as disclosed in U.S. Pat. No. 4,897,377)
generally have good dye up-take properties when used for thermal
dye transfer; however, they exhibit severe fade when the dye images
are subjected to high intensity daylight illumination. Polyesters
formed from alicyclic diesters are disclosed in U.S. Pat. No.
5,387,571 of Daly, the disclosure of which is incorporated by
reference. These alicyclic polyesters also generally have good dye
up-take properties, but their manufacture requires the use of
specialty monomers which add to the cost of the receiver element.
Polyesters formed from aliphatic diesters generally have relatively
low glass transition temperatures, which frequently results in
receiver-to-donor sticking at temperatures commonly used for
thermal dye transfer. When the donor and receiver are pulled apart
after imaging, one or the other fails and tears and the resulting
images are unacceptable.
U.S. Pat. No. 5,302,574 to Lawrence et al. discloses a
dye-receiving element for thermal dye transfer comprising a support
having on one side thereof a dye image-receiving layer, wherein the
dye image-receiving layer comprises a miscible blend of an
unmodified bisphenol-A polycarbonate having a number molecular
weight of at least about 25,000 and a polyester comprising
recurring dibasic acid derived units and diol derived units, at
least 50 mole % of the dibasic acid derived units comprising
dicarboxylic acid derived units containing an alicyclic ring within
two carbon atoms of each carboxyl group of the corresponding
dicarboxylic acid, and at least 30 mole % of the diol derived units
containing an aromatic ring not immediately adjacent to each
hydroxyl group of the corresponding diol or an alicyclic ring.
Thus, the alicyclic polyesters were found to be compatible with
high molecular weight polycarbonates.
U.S. Pat. No. 4,908,345 to Egashira et al. discloses a dye
receiving layer comprising a phenyl group (e.g. bisphenolA)
modified polyester resin synthesized by the use of a polyol having
a phenyl group as the polyol compound. U.S. Pat. No. 5,112,799,
also to Egashira et al., discloses a dye-receiving layer formed
primarily of a polyester resin having a branched structure.
Polymers may be blended for use in the dye-receiving layer in order
to obtain the advantages of the individual polymers and optimize
the combined effects. For example, relatively inexpensive
unmodified bisphenol-A polycarbonates of the type described in U.S.
Pat. No. 4,695,286 may be blended with the modified polycarbonates
of the type described in U.S. Pat. No. 4,927,803 in order to obtain
a receiving layer of intermediate cost having both improved
resistance to surface deformation which may occur during thermal
printing and to light fading which may occur after printing.
It would be highly desirable to provide an image recording element
with an image-receiving layer comprising a polymer composition
capable of providing excellent image properties. It would also be
desirable for the image-receiving layer to be readily applied to
the underlying support without inadequate adhesion problems. It
would be further desirable to provide such an image recording
element in which the dye-image layer is extrudable. It would be
still further desirable if a tie layer for adhering the
image-receiving layer to the support for the recording element
could provide not only improved adhesion but additionally provide
antistat properties to the recording element.
SUMMARY OF THE INVENTION
This invention relates to a process for making an image-recording
element, for example, a dye-receiving element for thermal dye
transfer, that includes a support having on one side thereof an
image-receiving layer wherein between the image-receiving layer and
the support is a tie layer comprising an optional
polyolefin-containing binder and a thermoplastic antistat polymer.
In particular, the invention relates to a method of forming a
multilayer film for use in an image recording element, which
multilayer (i.e., composite) film comprises at least two layers, a
surface layer and a tie layer directly adjacent the surface layer.
The process comprises (a) forming a first melt of a polymer for a
surface layer and a second melt comprising a thermoplastic antistat
polymer in an optional polymeric binder; (b) coextruding at least
the two melts onto a polyolefin support; (c) stretching the
coextruded layers to reduce the thickness; (d) applying the
coextruded melts to a support while simultaneously reducing the to
below the Tg of the composition of the surface layer. The melt for
the tie-layer composition, comprising both antistat polymer and
optional binder, preferably exhibits a viscosity that is not more
than 10 times or less than 1/10 that of the melt for the surface
layer when extruded with at least the first layer; and the peel
strength, in Newtons/meter, of said surface layer in contact with
the tie layer is at least twice the peel strength in the absence of
the tie layer.
The present invention is applicable to the manufacture of an image
recording element, including those used in thermal dye transfer
processes, electrophotography, or other printing techniques,
wherein an image is printed on a thermoplastic image-receiving
layer, whether dye, pigment, or toner is employed as the colorant
or ink. In one embodiment, a dye-receiver element in accordance
with the present invention exhibits excellent lightfade and high
dye transfer efficiency, as well as low materials cost.
DETAILED DESCRIPTION
The present invention relates to a process for making a multilayer
film, useful in an image recording element, which multilayer film
comprises a support and an outer or surface layer wherein between
the support and the outer layer is an "antistat tie layer"
comprising a thermoplastic antistat polymer or composition having
preselected antistat properties, adhesive properties, and
viscoelastic properties. In one embodiment of the invention, such a
multilayer film is used in making a thermal-dye-transfer
dye-receiver element comprising a support and an dye-receiving
layer wherein between the support and the dye-receiving layer is a
tie layer.
In particular, one aspect of the innovation relates to a process of
forming a multilayer film comprising at least two layers, a surface
layer and a tie layer directly adjacent the surface layer, wherein
the process comprises (a) forming a first melt, for the surface
layer, comprising a first polymeric binder, (b) forming a second
melt, for the tie layer, comprising a thermoplastic antistat
polymer in an optional second polymeric binder, wherein the second
melt exhibits a viscosity that is not more than 10 times or less
than 1/10 that of the first melt during the following extrusion
step; (c) coextruding the two melts to form a composite film; (d)
stretching the composite film to reduce its thickness; and (e)
applying the stretched composite film to a support while
simultaneously reducing the temperature of the composite film below
the Tg of the surface layer.
Preferably, the composition of the tie layer comprises a
polyolefin-containing binder and a thermoplastic antistat polymer.
Preferably, also, the peel strength, in Newtons/meter, of said
surface layer and support in contact with the tie layer is at least
twice the peel strength in the absence of the tie layer. The
antistat polymer exhibits a volume resistivity of 10.sup.5 to
10.sup.11 Ohms per square, preferably 10.sup.6 to 10.sup.12 Ohms
per square. Preferably the viscosity of the dye-receiving layer
melt composition is 100 to 10,000 poise at 1 sec.sup.-1 shear rate
at a temperature between 100 and 300.degree. C.
Peel strength is a measurement or method to assess the interlayer
adhesion. Peel strength can be assessed as follows. An image
receiving layer of a multilayer receiver sample is glued to a firm
surface. A tape is applied to the other exposed surface and then
peeled away. Peeling is accomplished by gripping the tape, bending
it through a 90 angle until it can be pulled away (peeled) in a
direction parallel to the film surface. All tests are performed in
a standard environment of 50% RH and 23C. The films are peeled
using an IMASS SP-2000 Slip/Peel Tester or the equivalent. The
crosshead speed was 5.1 mm/sec. The sample size is 2.54
cm.times.15.2 cm. Four specimens are tested per support sample. For
a tie layer, the range of adhesion in Newtons/meter is preferably
3-114 Newtons/meter.
In the preferred embodiment, the antistat polymer is a block
polymer which has a structure such that blocks of a polyolefin and
blocks of a hydrophilic polymer are bonded together alternately and
repeatedly. Preferably, the blocks of the hydrophilic polymer are
polyether blocks. The polyether blocks can be formed from one or
more alkylene oxides having 2 to 4 carbon atoms. The polyether
blocks can comprise ethylene oxide, propylene oxide, or butylene
oxide, or combinations thereof, preferably comprising at least 50
mole % ethylene oxide in the polyoxyalkylene chains. Typically, the
polyolefins are obtained by polymerization of one or a mixture of
two or more olefins containing 2 to 30 carbon atoms, preferably
containing 2 to 12 carbon atoms, particularly preferably propylene
and/or ethylene. Alternatively, low molecular weight polyolefins
can be obtained by thermal degradation of high molecular weight
olefins. The number average molecular weight of the polyolefin is
preferably 800 to 20,000.
In one embodiment, the antistat polymer is a block polymer having a
structure such that the polyolefin block and the polyether block
are bonded together alternately and repeatedly such that the
polymers have a repeating unit represented by the following general
formula (1). ##STR1##
In the general formula (I), n is an integer of 2 to 50, one of
R.sup.1 and R.sup.2 is a hydrogen atom and the other is a hydrogen
atom or an alkyl group containing 1 to 10 carbon atoms, y is an
integer of 15 to 800, E is the residue of a diol after removal of
the hydroxyl groups, A is an alkylene group containing 2 to 4
carbon atoms, m and m' each represents an integer of 1 to 300, X
and X' are connecting groups used in the synthesis of the block
polymer as listed in EP 1167425 A1, hereby incorporated by
reference in its entirety.
Such a block copolymer can be formed by the reaction of a mixture
comprising a modified polyether and a modified polyolefin. For
example, one or more polyether reactants such as polyether diols
can be reacted with polyolefin reactants (obtained by modifying the
termini of the polyolefin with carbonyl-containing groups or the
like) and a polycondensation polymerization reaction carried out
generally at 200 to 250.degree. C. under reduced pressure employing
known catalysts such as zirconium acetate.
Preferably, the antistat polymer comprises a block copolymer of
polyethylene oxide polyether segments with a polypropylene and/or
polyethylene polyolefin segments. In one embodiment, the block
polymer has a number average molecular weight of 2,000 to 200,000
as determined by gel permeation chromatography. The polyolefin of
the block polymer may have carbonyl groups at both polymer termini
and/or a carbonyl group at one polymer terminus.
A preferred material for the antistat tie layer is PELLESTAT 300
polymer, commercially available from Sanyo Chemical Industries,
Ltd. (Tokyo) or Tomen America, Inc. (New York, N.Y.). The antistat
polymer PELLESTAT 300 (a copolymer of a polyether and a polyolefin)
is described in EP 1167425 A1. The antistat polymers comprising a
polyolefin with polyether segments are preferred, for example a
(propylene or polyethylene oxide (polyether) copolymer with
polypropylene or polyethylene(polyolefin) and polypropylene 70:30.
Such an antistat polymer is a block polymer which has a structure
such that blocks of a polyolefin and blocks of a hydrophilic
polymer having a volume resistivity of 10.sup.5 to 10.sup.11 Ohms
per square are bonded together alternately and repeatedly.
Typically, the block polymer has a number average molecular weight
of 2,000 to 60,000 as determined by gel permeation
chromatography.
The preferred antistat polymers such as PELLESTAT 300 do not
require a compatibilizer and, therefore, compatibilizers can be
substantially absent from the tie layer. Other antistat polymers
may require a compatibilizer to obtain the necessary miscibility
with polyolefins, as will be understood by the skilled artisan.
Compatibilizers are typically low molecular weight polymers with
functional groups that are compatible with both the antistat
polymer and the binder polymer which are otherwise immiscible or
non-compatible. The compatibilizer allows the antistat polymer and
the binder to be uniformly dispersed. Examples of such antistat
polymers are polyether-block copolyamide, a polyetheresteramide,
and segmented polyether urethanes.
Other materials that can be used to make an antistat tie layer
include PEBAX (commercially available from Atofina (Finland), which
material is copolymer of polyether and polyamide. Such copolymers
may be admixed with an alternative polymer, such as polyolefin, if
a suitable compatibilizer is utilized, for example, to provide the
desired viscoelastic properties.
Still other materials known in the art that can be melt processed
while retaining their antistatic activity and overall physical
performance are various polymeric substances containing a high
concentration of polyether blocks. Ionic conduction along the
polyether chains makes these polymers inherently dissipative,
yielding surface resistivities in the range 10.sup.8 to 10.sup.13
Ohms per square. Examples of such ionic conductors are:
Polyether-block-copolyamide (e.g., as disclosed in U.S. Pat. Nos.
4,115,475; 4,195,015; 4,331,786; 4,839,441; 4,864,014; 4,230,838;
4,332,920; and 5,840,807), Polyetheresteramide (e.g., as disclosed
in U.S. Pat. Nos. 5,604,284; 5,652,326; 5,886,098), and a
thermoplastic polyurethane containing a polyalkylene glycol moiety
(e.g., as disclosed in U.S. Pat. Nos. 5,159,053 and 5,863,466).
Such inherently dissipative polymers (IDPs) have been shown to be
fairly thermally stable and readily processable in the melt state
in their neat form or in blends with other thermoplastic materials.
Most of the known inherently conductive polymers (ICPs), such as
polyaniline, polypyrrole and polythiophene, are not usually
sufficiently thermally stable to be used in this invention.
However, if the ICPs are thermally stabilized and are able to
retain their electro-conductive properties after melt processing at
elevated temperatures, they could also be applied in this
invention. Such polymers are described further in U.S. Pat. No.
6,207,361 to Greener. Such polyetheresteramides, polyether block
copolyamides and segmented polyether urethanes, in admixture with
appropriate compatibilizers are useful in the present
invention.
Any compatibilizer which can ensure compatibility between the
polyether polymeric antistat (component A) and the extrudable
polymer (component B) by way of controlling phase separation and
polymer domain size can be employed. Some exemplary compatibilizers
are described in U.S. Pat. No. 6,436,619 to Majumdar et al. hereby
incorporated by reference. Some examples of compatibilizers are:
polyethylene, polypropylene, ethylene/propylene copolymers,
ethylene/butene copolymers, all these products being grafted with
maleic anhydride or gycidyl methacrylate; ethylene/alkyl
(meth)acrylate/maleic anhydride copolymers, the maleic anhydride
being grafted or copolymerized; ethylene/vinyl acetate/maleic
anhydride copolymers, the maleic anhydride being grafted or
copolymerized; the two above copolymers in which anhydride is
replaced fully or partly by glycidyl methacrylate;
ethylene/(meth)acrylic acid copolymers and optionally their salts;
ethylene/alkyl (meth)acrylate/glycidyl methacrylate copolymers, the
glycidyl methacrylate being grafted or copolymerized, grafted
copolymers constituted by at least one mono-amino oligomer of
polyamide and of an alpha-mono-olefin (co)polymer grafted with a
monomer able to react with the amino functions of said oligomer.
Such compatibilizers are described in, among others, EP-A-0,342,066
and EP-A-0,218,665 which are also incorporated herein by reference.
Some preferred compatibilizers are terpolymers of ethylene/methyl
acrylate/glycidyl methacrylate and copolymers of ethylene/ glycidyl
methacrylate, commercially available as Lotader from Atofina or
similar products. Preferred compatibilizers also include maleic
anhydride grafted or copolymerized polyolefins such as
polypropylene, polyethylene, etc., commercially available as Orevac
from Atofina or similar products.
According to one embodiment of the invention, the antistat tie
layer and the outer layer (or dye-receiving layer) can be
coextruded as follows. In a first step, a first melt and a second
melt are formed, the first melt of a polymer being for an outer
layer (or dye-image receiving layer) and the second melt comprising
a thermoplastic antistat polymer having desirable adhesive and
viscoelastic properties, preferably having not more than 10 times
or 1/10, preferably not more than 3 times or less than 1/3
difference in viscosity from that of the first melt that forms the
outer layer (or dye-receiving layer), thereby promoting efficient
and high quality coextrusion. The tie layer, and its melt,
preferably comprises a polymeric binder or matrix for the antistat
polymer. The polymer binder can help to obtain the desired
viscoelastic properties of the tie-layer melt, so that when
extruded, the film does not extend beyond the edges of the
coextruded film from the melt for the image-receiving layer,
resulting in unmatched films. In such an event, a portion of an
unmatched extruded film may be trimed off. However, this reduces,
although not eliminating, the favorable economics for extrusion
versus solvent coating. Unmatched edges between coextruded films
may tend to occur when the viscosity ratio between coextruded melts
is about 10:1. In comparison, if the ratio is reduced to about 3:1,
for example by adding a binder to a Pellestat.RTM. antistat
polymer, then the entire width of the films can be used without any
trimming. The need or advantage for a polymer binder may be reduced
or eliminated, however, if any of the following criteria are true:
(1) the antistat polymer is sold at a higher molecular weight and,
therefore, is inherently more viscous so that the melt for the tie
layer exhibits a viscosity closer to that of the melt for the
image-receiving layer; (2) the coating machine is narrower (for
example, 12" vs 44"); (3) the viscosity of the image-receiving
layer is reduced so that it matches that of the antistat polymer
more closely; and/or (4) a multi-manifold die which introduces the
polymer layers at the last possible second, ensuring greater
uniformity. However, since the latter mechanical set up is
relatively expensive, it may be preferred to use a coextrusion
feedblock that mixes the polymers further upstream from the die
lips. In a second step, the two melts are coextruded. In a third
step, the coextruded layers or laminate is stretched to reduce the
thickness. In a third step, the extruded and stretched melt is
applied to a support for the image recording element or
dye-receiving element while simultaneously reducing the temperature
within the range below the Tg of the dye image receiving layer, for
example, by quenching between two nip rollers. In a preferred
embodiment, the support is a polyolefin-containing support.
A preferred embodiment of the invention is directed to a method of
making a dye-receiving element for thermal dye transfer comprising
a support and on one side thereof a dye image-receiving layer,
wherein between the dye-image receiving layer and the support is a
tie layer that was made by coextrusion with at least the
dye-receiving layer, wherein the composition of the tie layer
comprises a polyolefin-containing binder and a thermoplastic
antistat polymer having preselected antistat, adhesive, and
viscoelastic properties as described above. The total thickness of
said dye-receiving layer in the final product is less than 10
microns, preferably 1 to 5 microns thick; the thickness of the tie
layer is also preferably not more than 10 microns, preferably 1 to
5 microns thick.
In one preferred embodiment, the support for the dye-receiving
element comprises a compliant substrate sheet over a base support
and the support further comprises a backing layer on the base
support.
The dye-receiver element can be made by a process comprising first
forming a first melt of a polymer for a dye image receiving and a
second melt comprising a thermoplastic antistat polymer in a
polymeric matrix, secondly, coextruding the two melts onto a
support, preferably comprising a polyolefin surface layer and,
thirdly, stretching the coextruded layers to reduce the thickness
uniaxially or biaxially, preferably uniaxially, for example, the
coextruded layers can be stretched from a thickness of about 500
micrometers to about 3 micrometers. The extruded melt can be
applied to a support for the dye-receiver element while
simultaneously reducing the temperature within the range below the
Tg of the dye image receiving layer, for example, by quenching
between two nip rollers, wherein the tie-layer composition is as
described above. Preferably, the support is a moving web and the
film extruded over the moving web at a speed 30 meters per minute
or more.
The particular structure of a dye-receiver element made according
to the present invention can vary, but is generally a multilayer
structure comprising, under the dye-image receiving layer, a
support (defined as all layers below the dye-image receiving layer,
not including any tie layer immediately adjacent the dye-image
receiving layer) that comprises a composite compliant film,
preferably comprising a microvoided layer, and (under the compliant
film) a base support, preferably comprising a cellulose paper or
resin coated paper.
A microvoided layer in the support can, for example, comprise
crosslinked microbeads or non-crosslinked polymer particles that
are immiscible with the polyester matrix of the microvoided layer.
A microvoided layer provides more compliant properties to the
receiver. This is important as it impacts the degree of contact to
the thermal head during printing. Higher compliance results in
better contact and higher dye transfer efficiency due to improved
thermal transfer.
In a preferred embodiment, beneath one or more microvoided layers
is a paper-containing base support, more preferably a resin-coated
paper support. In addition, subbing layers or additional tie layers
can be employed between adjacent layers within a section or between
sections of the dye-receiver element. Typically, the support is
greater than 100 micrometers, preferably greater than 200
micrometers, and most preferably 200 to 300 micrometers thick.
Typically, the entire receiver element has a total thickness of
from 20 to 400 micrometers, preferably 30 to 300 micrometers.
Typically, a support comprises cellulose fiber paper. Preferably,
the support is from 120 to 250 .mu.m thick and the applied
(extruded) composite film (tie layer and dye-image receiving layer)
is from 30 to 50 .mu.m thick. The support can further comprise a
backing layer, preferably a polyolefin backing layer on the side of
the support opposite to the composite film and a tie layer between
the support and the laminate film.
In one embodiment of the invention, the image receiving layer
comprises a polyester material. A preferred polyester comprises (a)
recurring dibasic acid derived units and polyol derived units, at
least 50 mole % of the dibasic acid derived units comprising
dicarboxylic acid derived units containing an alicyclic ring
comprising 4 to 10 ring carbon atoms, which ring is within two
carbon atoms of each carboxyl group of the corresponding
dicarboxylic acid, (b) 25 to 75 mole % of the polyol derived units
containing an aromatic ring not immediately adjacent to each
hydroxyl group of the corresponding diol or an alicyclic ring, and
(c) 25 to 75 mole % of the polyol derived units of the polyester
contain an alicyclic ring comprising 4 to 10 ring carbon atoms.
Such polyester polymers for use in a dye-receiving element having a
release agent according to the invention are condensation type
polyesters based upon recurring units derived from alicyclic
dibasic acids (Q) and diols (L) and (P) wherein (Q) represents one
or more alicyclic ring containing dicarboxylic acid units with each
carboxyl group within two carbon atoms of (preferably immediately
adjacent to) the alicyclic ring and (L) represents one or more diol
units each containing at least one aromatic ring not immediately
adjacent to (preferably from 1 to about 4 carbon atoms away from)
each hydroxyl group or an alicyclic ring which may be adjacent to
the hydroxyl groups.
As used herein, the terms "dibasic acid derived units" and
"dicarboxylic acid derived units," or "dicarboxylic acids' and
"diacids," are intended to define units derived not only from
carboxylic acids themselves, but also from equivalents thereof such
as acid chlorides, acid anhydrides, and esters for these acids, as
in each case the same recurring units are obtained in the resulting
polymer. Each alicyclic ring of the corresponding dibasic acids may
also be optionally substituted, e.g. with one or more C.sub.1 to
C.sub.4 alkyl groups. Each of the diols may also optionally be
substituted on the aromatic or alicyclic ring, e.g. by C.sub.1 to
C.sub.6 alkyl, alkoxy, or halogen. Regarding the polyol/diol
component (including all compounds having two or more OH or OH
derived groups, including diols, triols, etc.), the total mole
percentages for this component is equal 100 mole %. Similarly,
regarding the acid component (including all compounds/units having
two or more acid or acid-derived groups), the total mole
percentages for this component is equal to 100 mole %.
In a preferred embodiment, the polyester used in the dye-image
receiving layer comprises alicyclic rings in both the dicarboxylic
acid derived units and the polyol derived units that contain from 4
to 10 ring carbon atoms. In a particularly preferred embodiment,
the alicyclic rings contain 6 ring carbon atoms.
Such alicyclic dicarboxylic acid units, (Q), are represented by
structures such as: ##STR2## ##STR3##
The aromatic diols, (L), are represented by structures such as:
##STR4## ##STR5##
The alicyclic diols, (P), are represented by structures such as:
##STR6##
In the case of an extrudable polyester, it has been found
advantageous to employ monomers (as a replacement for either a
diacid and/or diol that has three or more functional groups,
preferably one more multifunctional polyols (N) or polyacids and
derivatives thereof (O) that can provide branching. Multifunctional
polyols, for example, include glycerin, 1,1,1-trimethylolethane,
and 1,1,1-trimethylolpropane, or combinations thereof. Polyacids
having more than two carboxylic acid groups (including esters or
anhydrides derivatives thereof) include, for example, trimellitic
acid, trimesic acid, 1,2,5-, 2,3,6- or 1,8,4-naphthalene
tricarboxylic anhydride, 3,4,4'-diphenyltricarboxylic anhydride,
3,4,4'-diphenylmethanetricarboxylic anhydride,
3,4,4'-diphenylethertricarboxylic anhydride,
3,4,4'-benzophenonetricarboxylic anhydride acid and derivatives
thereof. Multifunctional polyols or anhydrides, for example,
include compounds represented by structures such as: ##STR7##
A small amount of aromatics, introduced by inclusion of aromatic
diacids or anhydrides, is optional and is not preferred due to
their tendency to reduce imaged dye density. Examples include, but
are not limited to, terephthalic acid (S1) and isoterephthalic acid
(S2).
Additional Diacids R and diols M may be added, e.g., to precisely
adjust the polymer's Tg, solubility, adhesion, etc. Additional
diacid comonomers could have the cyclic structure of Q or be linear
aliphatic units or be aromatic to some degree. The additional diol
monomers may have aliphatic or aromatic structure but are
preferably not phenolic.
Some examples of suitable monomers for R include dibasic aliphatic
acids such as: R1: HO.sub.2 C(CH.sub.2).sub.2 CO.sub.2 H R2:
HO.sub.2 C(CH.sub.2).sub.4 CO.sub.2 H R3: HO.sub.2
C(CH.sub.2).sub.7 CO.sub.2 H R4: HO.sub.2 C(CH.sub.2).sub.10
CO.sub.2 H
Some examples of some other suitable monomers for M include diols
such as: M1: HOCH.sub.2 CH.sub.2 OH M2: HO(CH2)3OH M3:
HO(CH.sub.2).sub.4 OH M4: HO(CH.sub.2).sub.9 OH M5: HOCH.sub.2
C(CH.sub.3).sub.2 CH.sub.2 OH M6: (HOCH.sub.2 CH.sub.2).sub.2 O M7:
HO(CH.sub.2 CH.sub.2 O).sub.n H (where n=2 to 50)
The above-mentioned monomers may be copolymerized to produce
structures such as: ##STR8##
wherein o+q+r+s=100 mole percent (based on the diacid component)
and p+m+n+1=100 mole percent (based on the polyol component). With
respect to the diacid, preferably q is at least 50 mole percent, r
is less than 40 mole percent, and s is less than 10 mole percent.
With respect to the polyol, preferably p is 25 to 75 mole percent,
1 is 25 to 50 mole percent, and m is 0 to 50 mole percent. With
respect to the polyfunctional monomers (having more than two
functional groups), the total amount of n or o is preferably 0.1 to
10 mole percent, preferably 1 to 5 mole percent.
The polyesters of the invention preferably, except in relatively
small amounts, do not contain an aromatic diacid such as
terephthalate or isophthalate.
The polyester preferably has a Tg of from about 40 to about
100.degree. C. In a preferred embodiment of the invention, the
polyesters have a number molecular weight of from about 5,000 to
about 250,000, more preferably from 10,000 to 100,000.
In addition to the polymeric binder described above, the receiving
layer may also contain other polymer such as polycarbonates,
polyurethanes, polyesters, polyvinyl chlorides,
poly(styrene-coacrylonitrile), poly(caprolactone), etc. For use in
polyester-polycarbonate blends, examples of unmodified bisphenol-A
polycarbonates having a number molecular weight of at least about
25,000 include those disclosed in U.S. Pat. No. 4,695,286. Specific
examples include MAKROLON 5700 (Bayer AG) and LEXAN 141 (General
Electric Co.) polycarbonates. ##STR9##
Lexan.RTM. 141: p.about.120, Tg.about.150.degree. C.
Makrolon.RTM. 5700: p.about.280, Tg.about.157.degree. C.
In the case of blends with a polycarbonate, the polycarbonate
preferably has a Tg of from about 100 to about 200.degree. C., in
which case the polyester preferably has a lower Tg than the
polycarbonate, and acts as a polymeric plasticizer for the
polycarbonate. The Tg of the final polyester/polycarbonate blend is
preferably between 40.degree. C. and 100.degree. C. Higher Tg
polyester and polycarbonate polymers may be useful with added
plasticizer.
In one embodiment of the invention, a polyester polymer is blended
with an unmodified bisphenol-A polycarbonate and at a weight ratio
to produce the desired Tg of the final blend and to minimize cost.
Conveniently, the polycarbonate and polyester polymers may be
blended at a weight ratio of from about 90:10 to 10:90, preferably
80:20 to 20:80, more preferably from about 75:25 to about
25:75.
The following polyester polymers E-1 through E-14, comprised of
recurring units of the illustrated monomers, are examples of
polyester polymers usable in the receiving layer polymer blends of
the invention.
E-1 through E-3: A polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol,
4,4'-bis(2-hydroxyethyl)bisphenol-A and
2-ethyl-2-(hydroxymethyl)-1,3-propanediol ##STR10## E-1: x=48 mole
% y=50 mole % z=2 mole % E-2: x=46 mole % y=50 mole % z=4 mole %
E-3: x=44 mole % y=50 mole % z=6 mole %
E-4 through E-6: A polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol,
4,4'-bis(2-hydroxyethyl)bisphenol-A and glycerol ##STR11## E-4:
x=48 mole % y=50 mole % z=2 mole % E-5: x=46 mole % y=50 mole % z=4
mole % E-6: x=44 mole % y=50 mole % z=6 mole %
E-7 through E-8: A polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid, 1,4-cyclohexanedimethanol,
4,4'-bis(2-hydroxyethyl)bisphenol-A and pentaerythritol ##STR12##
E7: x=48 mole % y=50 mole % z=2 mole % E-8: x=46 mole % y=50 mole %
z=4 mole %
E-9 through E-11: A polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid, trimellitic anhydride,
1,4-cyclohexanedimethanol and 4,4'-bis(2-hydroxyethyl)bisphenol-A.
##STR13## E-9: q=98 mole % o1=2 mole % x=50 mole % y=50 mole %
E-10: q=98 mole % o1=4 mole % x=50 mole % y=50 mole % E-11: q=94
mole % o1=6 mole % x=50 mole % y=50 mole %
E-12 through E-14: A polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid, pyromellitic anhydride,
1,4-cyclohexanedimethanol and 4,4'-bis(2-hydroxyethyl)bisphenol-A.
##STR14## E-12: q=98 mole % o2=2 mole % x=50 mole % y=50 mole %
E-13: q=96 mole % o2=4 mole % x=50 mole % y=50 mole % E-14: q=94
mole % o2=6 mole % x=50 mole % y=50 mole %
The following Table summarizes the various polyesters that are used
as the binder in the dye-image receiving layer in preferred
embodiments of the invention.
Alicyclic Aromatic Additional Branching Alicyclic Diacid Anhydride
Glycol Glycol Glycol Agent Mole % Cmpd Mole % Q Mole % O Mole % X
Mole % Y Mole % M M1, M2, M3 C-1 100 0 50 50 0 0 C-2 100 0 30 50 M2
= 20 0 C-3 100 0 25 50 M6 = 25 0 E-1 100 0 49 50 0 N1 = 1 E-2 100 0
48 50 0 N1 = 2 E-3 100 0 47 50 0 N1 = 3 E-4 100 0 49 50 0 N2 = 1
E-5 100 0 48 50 0 N2 = 2 E-6 100 0 47 50 0 N2 = 3 E-7 100 0 49 50 0
N3 = 1 E-8 100 0 48 50 0 N3 = 2 E-9 98 O1 = 2 50 50 0 0 E-10 98 O1
= 4 50 50 0 0 E-11 96 O1 = 6 50 50 0 0 E-12 98 O2 = 2 50 50 0 0
E-13 96 O2 = 4 50 50 0 0 E-14 94 O2 = 6 50 50 0 0
The following polymers C-1, C-2, and C-3 shown below are for
comparison to the polymers of the invention.
C-1: Polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid,
4,4'-bis(2-hydroxyethyl)bisphenol-A and 1,4-cyclohexanedimethanol.
##STR15## C-1: x=50 mole % m=50 mole %
(mole % based on total monomer charge of acid and glycol
monomers)
C-2: Polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid,
4,4'-bis(2-hydroxyethyl)bisphenol-A, 1,4-cyclohexanedimethanol and
2,2'-oxydiethanol. ##STR16## C-2: x=25 mole % y=50 mole % m2=25
mole %
C-3: Polymer considered to be derived from
1,4-cyclohexanedicarboxylic acid,
4,4'-bis(2-hydroxyethyl)bisphenol-A, 1,4-cyclohexanedimethanol and
1,3-propanediol ##STR17## C-3: x=30 mole % y=50 mole % m1=20 mole
%
The image-receiving layer may be present in any amount which is
effective for its intended purpose. In general, good results have
been obtained at a receiving layer concentration of from about 0.5
to about 20 g/m.sup.2., preferably 1 to 15 g/m.sup.2, more
preferably 3 to 10 g/m.sup.2.
The receiving layer of the invention may also contain a release
agent, such as a silicone or fluorine based compound, as is
conventional in the art. Resistance to sticking during thermal
printing may be enhanced by the addition of such release agents to
the dye-receiving layer or to an overcoat layer. Various releasing
agents are disclosed, for example, in U.S. Pat. No. 4,820,687 and
U.S. Pat. No. 4,695,286, the disclosures of which are hereby
incorporated by reference in their entirety.
A preferred release agent, especially for an extruded dye-receiving
layer, are ultrahigh molecular weight silicone-based compounds.
Preferably, the weight average molecular weight of the compound or
polymer should be at least 100,000, more preferably at least
500,000, most preferably at least 1,000,000, for example, between
1,000,000 and 5,000,000. The silicone release agent should be as
compatible as possible with the polymers used in the dye receiving
layer. When the dye-receiving layer contains a polycarbonate, it is
preferred for the release agent to have hydroxy terminal groups to
improve the compatibility of the silicone compound in the
polycarbonate-containing blend.
High or ultrahigh molecular weight silicone release agents are
commercially available, for example, from Dow Coming (Midland,
Mich.), including MB50-315 and MB-010. MB50-315 is a
hydroxy-terminated dimethyl siloxane polymer. However, depending on
the composition of the dye-receiving layer, organic end groups may
be used, for example, including methyl and phenyl.
MB50-315 silicone material is commercially available as a 50 weight
percent mixture of pelletized solid polydimethylsiloxane dispersed
in polycarbonate polymer. Depending on the composition of the
dye-receiving layer, other dispersions may be preferred, for
example, MB50-010 from Dow Coming which is a dispersion in
polyester. Suitably, the release agent is used in amounts of 0.5 to
10 percent, preferably 2 to 10, most preferably 3 to 8 percent, by
weight solids in the dye-receiving-layer composition. Some of the
release agent may be lost during manufacture of the dye-receiving
element. Typically, a sufficient portion of the release agent will
migrate to the surface of the dye-receiving layer to prevent
sticking during thermal dye transfer. Siloxane release agents are
disclosed in concurrently filed copending commonly assigned U.S.
Ser. No. 10/376,186 of Arrington et al., hereby incorporated by
reference.
A plasticizer may also be present in the dye image-receiving layer
in any amount which is effective for the intended purpose. In
general, good results have been obtained when the plasticizer is
present in an amount of from about 3 to about 100%, preferably from
about 4 to about 30%, based on the weight of the polymeric binder
in the dye-image receiving layer.
In one embodiment of the invention, an aliphatic ester plasticizer
is employed in the dye-image receiving layer. Suitable aliphatic
ester plasticizers include both monomeric esters and polymeric
esters. Examples of aliphatic monomeric esters include ditridecyl
phthalate, dicyclohexyl phthalate and dioctylsebacate. Examples of
aliphatic polyesters include polycaprolactone, poly(butylene
adipate) and poly(hexamethylene sebacate).
In a preferred embodiment of the invention, the monomeric ester is
dioctylsebacate. In another preferred embodiment, the aliphatic
polyester is poly(1,4-butylene adipate) or poly(hexamethylene
sebacate).
U.S. Pat. No. 6,291,396 to Bodem et al. discloses various aliphatic
ester plasticizer, including polyesters or monomeric esters.
Phthalate ester plasticizers are disclosed in U.S. Pat. No.
4,871,715 to Harrison et al., which plasticizers may be used in a
receiving layer alone or as mixtures.
In the case of dye-receiving layers made by extruding rather than
by solvent coating the dye-receiving layer, then it has been found
advantageous to include, as an additive to the composition of the
dye-receiving layer, a phosphorous-containing stabilizer. Thus, in
one embodiment of the invention, a thermal-dye-transfer receiving
element according to the present invention comprises an extrudable
composition for the receiving layer made from a
polycarbonate-polyester blend which contains a
phosphorous-containing stabilizer such as phosphorous acid or an
organic diphosphite such as bis(2-ethylhexyl)phosphite, to prevent
undue branching of the polyester polymer blend during high
temperature melt extrusion. The extruded receiving layer is applied
simultaneously with an extruded tie layer to a moving web
comprising a multilayer support. The phosphorous stabilizer can be
combined, for example, with a plasticizer such as dioctyl sebacate
or the like. Preferably, to improve compatibility, the plasticizer
is combined with the stabilizer prior to combining both with the
other components of the dye receiving layer.
U.S. Pat. No. 5,650,481 describes the use of polyester resins
prepared in the presence of a catalyst/stabilizer system containing
one or more phosphorous compounds. Included within the definition
of phosphorous compounds are phosphorus-based stabilizers such as
alkyl phosphates, aryl phosphates, inorganic phosphates,
phosphates, phosphoric acid and phosphoric acid esters, especially
phosphates and phosphoric acid, and phosphorous acid. Preferred in
the present invention are organic diphosphites, more preferably an
alkyl diphosphate, most preferably wherein the alkyl group has 1 to
11 carbon atoms.
Various polymerization catalysts can be used to make the
above-described polyesters for the dye-image receiving layer.
Optionally, a plurality of polymers may be blended for use in the
dye receiving layer in order to obtain the advantages of the
individual polymers and optimize the combined effect, as indicated
above. A problem with such a polymer blend, however, may result if
the polymers chemically transesterify with each other during
compounding and extrusion. A by-product of such a reaction may be
the liberation of carbon dioxide and the formation of yellow color
in the blend, which have a deleterious effect on the melt curtain
formed during the extrusion process. Both of these problems are
exacerbated by the use of titanium catalysts during the syntheses
of the polyester used in the blend. It has been found, therefore,
that the use of non-esterified diacids in the synthesis of the
polyester allows the use of tin and other less deleterious
catalysts than titanium, which catalysts, preferably coupled with
phosphorous stabilizers, help in the elimination of polymer
transesterification. Polyester/polycarbonate blends which exhibit
transesterification can not be effectively extruded. Use of diacids
with effective catalysts and stabilizers can help to eliminate this
adverse reaction.
Despite the fact that the diester monomer used in the synthesis of
the polyester is less expensive, requires less heat, and is general
more amenable to polymer preparation, it has, therefore, been found
unexpectedly advantageous for the polyester in the dye-image
receiving layer to be made employing, mainly or entirely, the
diacid monomers in the form of the diacid monomer instead of the
diester monomer and to employ tin or other non-titanium catalysts
as the polymerization catalyst. As mentioned above, the use of the
diacid and tin catalyst was able to prevent or minimize the
transesterification exacerbated by the titanium catalyst. Suitably
the catalyst is added in the amount of 0.01 to 0.08% by weight
solids to the polymerization composition.
The dye-image receiving layer can be applied to a support for the
receiver by a solvent coating process. In a preferred embodiment,
however, the dye-receiving layer, preferably both the dye-receiving
layer and a tie-layer, may be made by an extrusion process. Such a
process is described as follows. Prior to extruding the dye-image
receiving layer onto a substrate, the polyester material used to
make the dye receiving layer should be dried to reduce hydrolytic
degradation in the extrusion process. The drying process suitably
occurs at a temperature slightly below the glass transition
temperature of the polyester so that the polyester particles remain
free flowing through the dryer. Because the drying temperatures of
these polyester are so low, the use of desiccated gas or vacuum is
preferred. For example, for a polyester with a glass transition
temperature of 56.degree. C., a drying temperature of 43.degree. C.
for 12 hours using air with a dewpoint of -40.degree. C. in a
NOVATEC CDM-250 dryer is found to be adequate.
The greater the drying time, the lower the loss in molecular weight
and viscosity. Since higher molecular weight results in extrusion
temperatures which are higher, more drying is advantageous.
Typically, the higher the extrusion temperature, the less melt
viscosity present and the higher the extrusion speed during
commercial manufacture.
The polycarbonates used in this embodiment, such as LEXAN 151 from
GE Plastics should also be dried prior to use. The polycarbonate,
for example, is suitably dried at 120.degree. C. for 2 to 4
hours.
If a polycarbonate based released agent is used, such as Dow
Corning MB50-315 siloxane, then this material can be premixed into
the polycarbonate at the proper ratio, and dried under the same
conditions as the polycarbonate.
In one embodiment of a process according to the present invention,
all of the components of the dye receiving layer are melt mixed in
a compounding operation. To achieve adequate distributive and
dispersive mixing, a twin screw co-rotating mixer is typically
used, although a counter-rotating mixer, or kneader may also be
appropriate. These mixers can be purchased from a variety of
commercial vendors including Leistritz, Werner & Pfleiderer,
Buss, and other companies.
The order of addition of the materials into a compounder is
preferably as follows. The polycarbonate and the polyester are
added separately to prevent or minimize the formation of a network
that can reduce the ease of extrusion of the dye receiving layer,
and to minimize the propensity for donor-receiver sticking. If the
polycarbonate is sequentially added first, it is recommended that a
stabilizer, such as phosphorous acid or bis-ethyl hexyl phosphite
is added and well mixed in the polycarbonate before addition of the
polyester. This reduces network formation. Similarly, if the
polyester is added first, then is desirable that a stabilizer is
well mixed into the polyester before the addition of the
polycarbonate.
At the ports of the compounder where solids are introduced, the
screw should be designed to convey the solids away from the feeder,
then melt them, then mix them into the rest of the components. At
the point where the solids enter the compounder, it must also be
easy to allow entrained air to escape. We prefer to use the
sequence of conveying elements, kneading blocks, and reversing
elements at any solids addition. This gives an acceptable
combination of distributive and dispersive mixing, melting, and air
elimination. Where the liquid is injected into the extruder, the
use of gear elements is advantageous. These have excellent
distributive mixing characteristics. If the optional vacuum port is
used, conveyance elements with reverser elements on both sides is
used. The purpose of the reversers is to form a melt seal so that a
vacuum can be maintained in the extruder. Finally, conveyance
elements are used to build up pressure using a drag flow mechanism
so that the combined die receiving layer can be extruded through
the strand die into the water bath.
As indicated above, in terms of order of addition, there is a
choice between adding the polyester first or the polycarbonate
first (with the understanding that the stabilizer is added with the
first material, or between materials). Since the polycarbonate has
a much higher processing temperature, it is preferable to add this
to the extruder first. This is because it is easier to melt a low
melting material (polyester) into an already molten high melting
material (polycarbonate) than vice versa. When a first polymer is
added to another premelted second polymer, the mechanism of the
melting of the first polymer is largely due to heat transfer. Since
this is an inefficient way of melting a polymer, the higher melting
point polymer should usually be melted first.
The stabilizer does not necessarily have to be added with a liquid
plasticizer. At least two other techniques can be employed. If the
manufacturing rate is large enough, the stabilizer can simply be
added by itself. This can be accomplished with existing commercial
feeders if the overall compounding rate is on the order of 1000
kg/hr. If this rate is unreasonable, and other means of introducing
the stabilizer are desired, a stabilizer concentrate can be made
and introduced between the polyester or polycarbonate. The
disadvantage of using this technique is that the properties of the
stabilizer concentrate degrade rapidly with time, so the stabilizer
concentrate should be used immediately.
The melt temperature of the compounding operation should be kept
under 300.degree. C. to prevent crosslinking and thermal
degradation.
Since the amount of stabilizer which is added is often a small
number (0.01% to 1%), it is desirable that a convenient way be
found of adding the stabilizer so that the mass flow rate of the
stabilizer is high enough that commercially available equipment can
deliver it. Unless the process is run at very high rates, one
advantageous way to achieve this is by diluting the stabilizer in
another material so that the feed rates required become coincident
with commercially available equipment. Furthermore, it is extremely
convenient if the stabilizer is soluble in the liquid plasticizer
that is used, such as dioctyl sebacate.
The composition for the dye-receiving layer can be compounded in by
adding a mixture of the polycarbonate and a polycarbonate based
release agent in the first port of a twin screw extruder. Since
these materials are often in pellet form, a standard weight loss
feeder can be used. In a second port, located downstream from the
first port, a liquid plasticizer/stabilizer mixture can be added to
the twin screw extruder. The plasticizer/stabilizer mixture can be
held in a tank, which needs to be well stirred and at high
temperature if the plasticizer and stabilizer do not form
thermodynamically soluble solutions. The plasticizer/stabilizer
mixture is preferably pumped into the extruder using a positive
displacement reciprocating or centrifugal pump. A centrifugal pump
is most preferred, since this will give a more uniform flow of
material than a reciprocating pump. Positive displacement pumps
require a minimum pressure to pump against to assure uniform flow.
This pressure is achieved by pumping the liquid through a narrow
orifice prior to introducing it into the extruder.
Next, during compounding, the polyester is introduced in a third
port of the extruder, which is downstream from the second port.
Since the polyester can have a low glass transition temperature, it
may be necessary to cool this port using water cooling so the
polyester does not overheat. This allows the polyester to flow
freely into the extruder. However, cooling too much may cause
coagulation which would block the flow. In this third port,
provision should be made for the air entrained in the polyester
pellets, granules, or powder to escape. The polyester is most often
introduced in a screw fed side feeder, with an air vent on top. In
this instance, the side feeder must be water cooled. An optional
fourth port may exist in which a vacuum is applied. The purpose of
this vacuum is to remove volatiles from the system.
In accordance with the preferred embodiment, the melted material
for the dye-image receiving layer is then extruded from the exit of
the compounder through a strand die into warm water, which cools
the dye receiving layer enough to pelletize it downstream. If the
water is too cold, the melt strand becomes brittle and breaks in
the water bath. If the water is too warm, the melt strand becomes
too soft and cannot be pelletized correctly. The material can then
be pelletized into roughly rice sized particles which can later be
dried and fed into a single screw extruder for extrusion coating
the dye-receiving layer.
The pelletized composition for the dye-image receiving layer is now
preferably aged. This aging is manifested by the reduction of the
melt viscosity of the polymer with time. The measured melt
viscosity of the composition for the receiving layer could be up to
50% lower after one week of aging than when it is initially
manufactured. After approximately one week, the material ceases to
lose viscosity and stays relatively constant. If the material is
extrusion coated before it is aged, the melt viscosity, pressure
drop, and throughput could be undesirably variable. It is therefore
preferable to wait until the composition for the dye-image
receiving layer ("DRL") is adequately aged.
In the preferred process, then, the "DRL pellets", i.e., the
pellets for making the DRL or dye-image receiving layer, are
predried before extrusion. Since the glass transition temperature
of the pellets are often from 30-50.degree. C., it is difficult to
thoroughly dry them. It is therefore advantageous to use vacuum or
desiccated gases at low temperatures for long periods of time to
achieve the desired drying. If a desiccant dryer is used, it is
often found that during the desiccant recharge cycle the
temperature will spike above the glass transition temperature of
the air for a short period of time. This temperature spike,
however, is often enough to fuse the dye receiver pellets together,
and prevent the desired free flowing characteristics that
compounded pellets should have. To avoid this problem, it is
advisable to install a secondary heat exchanger to reduce the air
temperature during the desiccant recharge cycle.
Drying temperatures of above about 40.degree. C. for greater than
about 4 hours are typical. The dried material must then be conveyed
in a low moisture environment to the extruder. Dry air, nitrogen,
or vacuum feeding can all be used. The purpose of this low-moisture
condition is both to prevent the dye receiver pellets from
reacquiring moisture from the air, and to prevent condensation on
the pellets due to the cold feeder temperatures which follow.
The DRL pellets can have an unusual combination of low glass
transition temperature and low coefficient of friction due to the
release agent present in the formula. This combination of
properties may require different extrusion conditions from those
used in most commercial extrusion applications of olefins or
polyesters. The DRL polymer material will often preferentially
adhere to the extruder screw at a distance of one to five diameters
down the screw. The polymer material can build up and eventually
form a "slip ring", which is a cylindrical torroid adhering to the
screw. This torroid can then form a barrier that prevents other DRL
pellets from passing through the extruder. The result is that flow
stops, and polymer degrades inside the hot extruder for long
periods of time. Obviously, this is not a tolerable situation in a
steady state manufacturing operation. In order to alleviate this
problem, therefore, it is advantageous to keep the DRL pellets at a
temperature below the glass transition temperature until sufficient
pressure builds up in the extruder to "push" the pellets past the
point on the screw where they are inclined to build up. This can be
accomplished by cooling the first one to five diameters in length
with cooling water at about 20.degree. C. Both the extruder barrel
and the extruder screw are cooled. In addition, if the diameter of
the extruder is less than or equal to about 25 mm, the feed section
of the screw must be modified to increase the depth for feeding,
and to decrease the amount of heat transferred from the barrel to
the screw. The compression ratio of the screws used for extruding
the dye receiver pellets preferably has a compression ratio of more
than 5.0 if the diameter of the extruder is less than 25 mm.
After the initial cooling zone, the remainder of the extruder can
be run normally, for example, at a melt temperature between
230.degree. C. and 310.degree. C.
Meanwhile, according to the preferred embodiment of the process of
the invention, a substrate sheet, for under the dye-receiving
layer, is prepared comprising a microvoided composite film,
commercially available from Mobil, which substrate sheet is
laminated to the base support of the dye-receiver element of the
invention which base support may be a polymeric, a synthetic paper,
or a cellulose fiber paper support, or laminates thereof, as
indicated below. Preferred cellulose fiber paper supports include
those disclosed in Copending, commonly assigned U.S. Ser. No.
07/822,522 of Warner et al. the disclosure of which is incorporated
by reference.
When using a cellulose fiber paper base support, it is preferable
to extrusion laminate the microvoided composite films using a
polyolefin resin. During the lamination process, it is desirable to
maintain minimal tension of the microvoided packaging film in order
to minimize curl in the resulting laminated receiver support. The
back side of the paper support (i.e., the side opposite to the
microvoided composite film and receiving layer) may also be
extrusion coated with a polyolefin resin layer (e.g., from about 10
to 75 g/m.sup.2), and may also include a backing layer such as
those disclosed in U.S. Pat. Nos. 5,011,814 and 5,096,875, the
disclosures of which are incorporated by reference. For high
humidity applications (greater than 50% RH), it is desirable to
provide a backside resin coverage of from about 30 to about 75
g/m.sup.2, more preferably from 35 to 50 g/m.sup.2, to keep curl to
a minimum.
Thus, in order, from top to bottom, the dye-receiver element can
comprise a dye-image receiving layer, a substrate sheet primarily
(in terms of thickness) comprising a microvoided layer, and a base
support which is primarily not microvoided (preferably containing
paper), and a backing layer.
In one preferred embodiment, in order to produce receiver elements
with a desirable photographic look and feel, it is preferable to
use relatively thick paper supports (e.g., at least 120 .mu.m
thick, preferably from 120 to 250 .mu.m thick) and relatively thin
microvoided composite packaging films (e.g., less than 50 .mu.m
thick, preferably from 20 to 50 .mu.m thick, more preferably from
30 to 50 .mu.m thick).
If the dye-image receiving layer is extruded directly onto the
support, adhesion will be poor. Therefore, a tie layer as described
above may be used. Conventional tie-layer materials may be used for
the tie layer, including various polyolefins, LD polyethylene,
ethylene methacrylic acid, etc. However, it has been found
advantageous for a tie layer to also provide antistat properties in
addition to adhesive properties. This prevents the overall
structure from high static electricity, which would cause problems
with dust attraction and conveyance.
It has, therefore, been found advantageous to use a combination
adhesion/antistat layer (referred to herein as a "antistat tie
layer") with the dye-receiving layer of the present invention.
Optionally, this antistat tie layer may be coextruded with the dye
receiving layer.
As indicated above, a requirement for robust coextrusion is that
the viscosities of the materials roughly match. A rule of thumb is
that the ratio of viscosities should be less than about 3 to 1.
Unfortunately, the viscosity ratio of the material for the dye
receiving layer to the polyether polyolefin block copolymer is
about 10:1, which is difficult to coextrude, especially with a wide
extrusion die using a coextrusion feedblock. Applicants have found
that addition of a low-melt-rate thermoplastic such as
polypropylene with a melt flow rate of 1.9 g/10 min as measured by
ASTM Test Method D1238 or other thermoplastic polymer to the
polyether polyolefin copolymer helps both the viscosity matching
and the adhesion. A mixture consisting of about 20 to 80%,
preferably about 70% by weight, of the polyether polyolefin
copolymer with about 80 to 20%, preferably about 30% by weight, of
the polypropylene exhibits acceptable antistat properties, adhesion
and viscosity.
In one embodiment of the invention, an antistat tie layer is
preferably prepared by drying the above described PELLESTAT
polyether polyolefin block copolymer at an elevated temperature,
for example about 80.degree. C., for an extended time, for example,
about 4 hours or more. After drying, it can be dry blended with the
copolymer such as polypropylene, and added to a conventional single
screw extruder where it is preferably heated to a temperature of
between 230 and 310.degree. C.
The antistat tie layer and the dye receiving layer can then be
coextruded to form a laminate film. Coextrusion can be accomplished
employing a coextrusion feedblock or a multimanifold die, as
explained, for example, in Extrusion Coating Manual (4.sup.th Ed.
Tappi Press) pg. 48, hereby incorporated by reference. A
coextrusion feedblock is more versatile and less expensive, but a
multimanifold die can handle higher viscosity differences between
layers. A coextrusion feedblock can be operated so that the flow
pins are allowed to float freely, reaching equilibrium depending on
flow rate and kinematic viscosity.
The thickness ratio between the dye receiving layer and the
antistat tie layer can be chosen depending on a number of factors.
In terms of processing, the higher the thickness of the dye
receiving layer, the lower the draw resonance.
The dye-receiving layer preferably is extruded at a thickness of at
least 100 micrometers, preferably 100 to 800 micrometers, and then
uniaxially stretched to less than 10 microns, preferably 3-4
microns.
If an antistat tie layer is used, it may be difficult to control
the cross direction thickness uniformity because of the nature of
the material, particularly when the viscosity ratio of the
dye-receiving layer to the antistat tie layer is above about 5:1.
Therefore, a preferred ratio of less than 5:1, preferably about
3:1, is preferred.
After the layer ratio is adjusted in the coextrusion feedblock, the
tie layer and the dye-image receiving layer proceed to the extruder
die. The geometry of the die lip affects the overall quality of the
extruded product. Usually, the greater the die gap, the higher the
draw resonance. However if the die gap is too small, the pressure
drop will be excessive and melt fracture may result in an unsightly
feature called "shark skin". Also, the land length of the die can
affect the streakiness of the extruded product. The longer the land
length, the more streaky the product may appear. For the extrusion
step, a die gap from 0.25 to 1.0 mm, with a land length of about
2.5 mm is preferably employed.
After the tie layer/die receiving layer is coextruded, it can be
drawn down to a thickness of about 4 .mu.m by a nip, for example,
consisting of a rubber roll and larger metal roll. In the preferred
embodiment, a rubber roll and a metal roll is water cooled to avoid
excessive heat generation and to facilitate good release. The
temperature of the melt curtain can affect the ability to achieve a
robust coating. If the melt curtain is too hot, the melt strength
may be too low and the melt curtain may break. If the melt curtain
is too cold, then the melt curtain may break in brittle fracture.
Applicants have found a melt temperature of between 230.degree. C.
and 310.degree. C. provide advantageously good operating
characteristics. A coating speed of greater than 200 m/min is
easily attainable under these conditions.
Next, the extruded material is applied to the overall support
described above. The final product can be conveniently wound into a
roll and subsequently slit into sheets or rolls depending on the
specific printer the receiver element is being made for.
A dye-receiving element made in accordance with the present
invention can be used in a process of forming a dye transfer image
comprising imagewise-heating a dye-donor element comprising a
support having thereon a dye layer and transferring a dye image to
the dye-receiving element to form said dye transfer image.
Thermal printing heads which can be used to transfer dye from
dye-donor elements to receiving elements made by the present
process are available commercially. There can be employed, for
example, a Fujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal
Head F415 HH7-1089 or a Rohm Thermal Head KE 2OO8-F3.
Alternatively, other known sources of energy for thermal dye
transfer may be used, such as lasers as described in, for example,
GB No. 2,083,726A.
A dye-receiving element by the present process can be used in a
thermal dye transfer assemblage of the invention comprising a
dye-donor element, and the dye-receiving element, wherein the
dye-receiving element being in a superposed relationship with the
dye-donor element so that the dye layer of the donor element is in
contact with the dye image-receiving layer of the receiving
element.
When a three-color image is to be obtained, the above assemblage is
formed on three occasions during the time when heat is applied by
the thermal printing head. After the first dye is transferred, the
elements are peeled apart. A second dye-donor element (or another
area of the donor element with a different dye area) is then
brought in register with the dye-receiving element and the process
repeated. The third color is obtained in the same manner.
Dye-donor elements that are used with the dye-receiving element
made in accordance with process of the invention conventionally
comprise a support having thereon a dye-containing layer. Any dye
can be used in the dye-donor provided it is transferable to the
dye-receiving layer by the action of heat. Especially good results
have been obtained with sublimable dyes. Dye donors are described,
e.g., in U.S. Pat. Nos. 4,916,112, 4,927,803 and 5,023,228, the
disclosures of which are incorporated by reference.
As noted above, dye-donor elements are used to form a dye transfer
image. Such a process comprises imagewise-heating a dye-donor
element and transferring a dye image to a dye-receiving element as
described above to form the dye transfer image.
A dye-donor element can be employed which comprises a poly(ethylene
terephthalate) support coated with sequential repeating areas of
cyan, magenta and yellow dye, and the dye transfer steps are
sequentially performed for each color to obtain a three-color dye
transfer image. Of course, when the process is only performed for a
single color, then a monochrome dye transfer image is obtained.
Any dye can be used in the dye layer of the dye-donor element
provided it is transferable to the dye-receiving layer by the
action of heat. Especially good results have been obtained with
sublimable dyes. Examples of sublimable dyes include anthraquinone
dyes, e.g., Sumikaron Violet RS.RTM. (Sumitomo Chemical Co., Ltd.),
Dianix Fast Violet 3R FS.RTM. (Mitsubishi Chemical Industries,
Ltd.), and Kayalon Polyol Brilliant Blue N BGM.RTM. and KST Black
146.RTM. (Nippon Kayaku Co., Ltd.); azo dyes such as Kayalon Polyol
Brilliant Blue BM.RTM., Kayalon Polyol Dark Blue 2BM.RTM., and KST
Black KR.RTM. (Nippon Kayaku Co., Ltd.), Sumikaron Diazo Black
5G.RTM. (Sumitomo Chemical Co., Ltd.), and Miktazol Black 5GH.RTM.
(Mitsui Toatsu Chemicals, Inc.); direct dyes such as Direct Dark
Green B.RTM. (Mitsubishi Chemical Industries, Ltd.) and Direct
Brown M.RTM. and Direct Fast Black D.RTM. (Nippon Kayaku Co. Ltd.);
acid dyes such as Kayanol Milling Cyanine 5R.RTM. (Nippon Kayaku
Co. Ltd.); basic dyes such as Sumiacryl Blue 6G.RTM. (Sumitomo
Chemical Co., Ltd.), and Aizen Malachite Green.RTM. (Hodogaya
Chemical Co., Ltd.); ##STR18## ##STR19##
or any of the dyes disclosed in U.S. Pat. No. 4,541,830, the
disclosure of which is hereby incorporated by reference. The above
dyes may be employed singly or in combination to obtain a
monochrome. The dyes may be used at a coverage of from about 0.05
to about 1 g/m.sup.2 and are preferably hydrophobic.
A dye-barrier layer may be employed in the dye-donor elements to
improve the density of the transferred dye. Such dye-barrier layer
materials include hydrophilic materials such as those described and
claimed in U.S. Pat. No. 4,716,144.
The dye layers and protection layer of the dye-donor element may be
coated on the support or printed thereon by a printing technique
such as a gravure process.
A slipping layer may be used on the back side of the dye-donor
element to prevent the printing head from sticking to the dye-donor
element. Such a slipping layer would comprise either a solid or
liquid lubricating material or mixtures thereof, with or without a
polymeric binder or a surface-active agent. Preferred lubricating
materials include oils or semi-crystalline organic solids that melt
below 100.degree. C. such as poly(vinyl stearate), beeswax,
perfluorinated alkyl ester polyethers, poly-caprolactone, silicone
oil, poly(tetrafluoroethylene), carbowax, poly(ethylene glycols),
or any of those materials disclosed in U.S. Pat. Nos. 4,717,711;
4,717,712; 4,737,485; and 4,738,950. Suitable polymeric binders for
the slipping layer include poly(vinyl alcohol-co-butyral),
poly(vinyl alcohol-co-acetal), polystyrene, poly(vinyl acetate),
cellulose acetate butyrate, cellulose acetate propionate, cellulose
acetate or ethyl cellulose.
The amount of the lubricating material to be used in the slipping
layer depends largely on the type of lubricating material, but is
generally in the range of about 0.001 to about 2 g/m.sup.2. If a
polymeric binder is employed, the lubricating material is present
in the range of 0.05 to 50 weight %, preferably 0.5 to 40 weight %,
of the polymeric binder employed.
Any material can be used as the support for the dye-donor element
provided it is dimensionally stable and can withstand the heat of
the thermal printing heads. Such materials include polyesters such
as poly(ethylene terephthalate); polyamides; polycarbonates;
glassine paper; condenser paper; cellulose esters such as cellulose
acetate; fluorine polymers such as poly(vinylidene fluoride) or
poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such
as polyoxymethylene; polyacetals; polyolefins such as polystyrene,
polyethylene, polypropylene or methylpentene polymers; and
polyimides such as polyimide amides and polyetherimides. The
support generally has a thickness of from about 2 to about 30
.mu.m.
The process of the present invention is also useful for making
receiver sheets for electrostatographic imaging processes such as
electrophotography. In a conventional electrostatographic copying
process, a latent electrostatic image is formed on the insulating
surface of a photoconductor element. If a dry development process
is used, charged toner particles are applied to the electrostatic
image, where they adhere in proportion to the electrostatic
potential difference between the toner particles and the charges on
the latent image. Toner particles that form the developed image are
then transferred to a receiver sheet, where the transferred image
is fixed, usually by a thermal fusion process in which the receiver
sheet is passed between a pair of rollers under pressure and
subjected to temperatures of about 200-300.degree. F.
(93-149.degree. C.). It is conventional to transfer toner particles
from the photoconductor element to the image receiver sheet by
means of an electrostatic bias between the element and the receiver
sheet.
During transfer, the toner particles adhere to or become partially
embedded in the thermoplastic coating and are thereby more
completely removed from the photoconductor element. A further
improvement in toner transfer may be obtained by coating the
thermoplastic polymer layer on the receiver sheet with a release
agent. However, if the binder resin for the photoconductor and the
thermoplastic polymer layer of the receiver sheet are appropriately
selected with respect to their compositions and surface energies, a
release agent is not necessary.
Receiver sheets for electrophotographic toner images most often
comprise paper, although plastic sheets have also been used. U.S.
Pat. No. 4,795,676, the disclosure of which is incorporated herein
by reference, describes an electrostatic recording material
composed of a multi-layered synthetic paper support having an
electroconductive layer and a dielectric layer formed successively
thereon. The support has a base layer, with paper-like layers of
thermoplastic resin on both sides, and surface layers of
thermoplastic resin containing little if any inorganic fine powder.
Other patents describing alternative types of structures for
electrophotographic receiver elements include, for example, U.S.
Pat. No. 5,055,371 and U.S. Pat. No. 5,902,673, the disclosure of
which are incorporated herein by reference. For example, the latter
patent describes a toner image receiver sheet having a volume
resistivity of from 1.times.10.sup.8 Ohms per square to
1.times.10.sup.13 Ohms per square, preferably about
1.times.10.sup.10 ohms per square to 1.times.10.sup.12 ohms per
square. Volume resistivity within these ranges is desired to
produce the electrostatic bias between the photoconductor element
and the image receiver sheet required for efficient, complete
transfer of the toner image particles to the sheet. The toner image
receiver sheet cab comprise an opaque synthetic paper substrate and
a thermoplastic organic polymeric image-receiving layer disposed
thereon. In one embodiment, the receiver sheet has an
image-receiving layer polymer having a glass transition temperature
of about 40.degree. C. to 60.degree. C. and a thickness of about 1
micrometer to 30 micrometer, preferably a thickness of about 8
.mu.m to 12 .mu.m. The substrate suitably has a thickness of about
178 to 356 .mu.m.
The following examples are provided to further illustrate the
invention. The synthesis example is representative, and other
polyesters may be prepared analogously or by other methods know in
the art.
EXAMPLE 1
Polyester E-2 dried in a NOVATECH desiccant dryer at 43.degree. C.
for 24 hours. The dryer is equipped with a secondary heat exchanger
so that the temperature will not exceed 43.degree. C. during the
time that the desiccant is recharged. The dew point is -40.degree.
C.
LEXAN 151 polycarbonate from GE and MB50-315 silicone from Dow
Chemical Co. are mixed together in a 52:48 ratio and dried at
120.degree. C. for 2-4 hours at -40.degree. C. dew point.
Dioctyl Sebacate ('DOS) is preheated to 83.degree. C., and
phosphorous acid is mixed in to make a phosphorous acid
concentration of 0.4%. This mixture is maintained at 83.degree. C.
and mixed for 1 hour under nitrogen before using.
These materials are then used in the compounding operation. The
compounding is done on a LEISTRITZ ZSK 27 extruder with a 30:1
length to diameter ratio. The LEXAN-polycarbonate/MB50-315-silicone
material is introduced into the compounder first, and melted. Then
the dioctyl sebacate/phosphorous acid solution is added, and
finally the polyester is added. The final formula is 70.07%
polyester, 12.78% LEXAN 151 polycarbonate, 12% MB50-315 silicone,
5.13% DOS, and 0.02% phosphorous acid. A vacuum is applied with
slightly negative pressure, and the melt temperature is 240.degree.
C. The melted mixture is then extruded through a strand die, cooled
in 32.degree. C. water and pelletized. The pelletized dye receiver
is then aged for about 2 weeks.
The dye receiver pellets are then predried before extrusion, at
38.degree. C. for 24 hours in a NOVATECH dryer described above. The
dried material is then conveyed using desiccated air to the
extruder.
The tie layer is also compounded. PELESTAT 300 antistat polymer
from Sanyo Chemical Co. is predried in the above dryers at
77.degree. C. for 24 hours. It is then melt mixed in the above
compounder with undried HUNTSMAN P4G2Z-159 polypropylene
homopolymer in a 70/30 ratio at about 240.degree. C., then forced
through a strand die into 20.degree. C. water and pelletized. The
compounded tie-layer pellets are then dried again at 77.degree. C.
for 24 hours in a NOVATECH dryer, and conveyed using desiccated air
to the extruder.
The dye receiver pellets are then introduced into a liquid cooled
hopper which feeds a 6.3 cm single screw BLACK CLAWSON extruder.
This extruder has a 6.3 cm long cooling section in the beginning of
the extruder, which is cooled by 20.degree. C. water. The screw in
this machine is a standard compression screw with a single mixer.
The dye receiver pellets are melted in the extruder, and heated to
a temperature of 238.degree. C. The pressure is then increased
through a melt pump, and the melted DRL composition is pumped to a
CLEOREN coextrusion feedblock with AAABB configuration.
The tie-layer pellets are introduced into the liquid cooled hopper
of another 6.3 com single screw extruder of the above
configuration. The tie-layer pellets are also heated to a
238.degree. C. temperature, and then pumped to the CLEOREN
coextrusion feedblock.
The volumetric ratio of dye-receiving layer to tie layer is about
3:1. The dye-receiving layer and the tie layer are brought into
intimate contact in the CLOEREN feedblock, then pass into a
standard extrusion coating T die made by Cloeren. The die has a
slot of 0.8 mm, and a land length of 2.5 mm. The die forms a melt
curtain which travels 19 cm through the air before it is coated
onto the laminate support. The laminate support comprises a paper
core extrusion laminated with a 38 micron thick microvoided
composite film (OPPalyte.RTM. 350TW, Mobile Chemical Co.) as
disclosed in U.S. Pat. No. 5,244,861.
The melt curtain is immediately quenched in the nip between the
chill roll and the laminate. The chill roll is operated at
21.degree. C. At this point the thickness of the die receiving
layer is 3 .mu.m, and the thickness of the tie layer is 1
.mu.m.
The resultant coated paper is then wound onto a roll, and then
converted to the necessary dimensions for the thermal printing
operation.
EXAMPLE 2
To illustrate the effect of branching in the polyester according to
one aspect of the invention, two polyesters were made, one with no
branching agent (C-1, having the structure described above) and 2%
branching agent (E-2, having the structure described above). The
percentage is base on the polyol-monomer component of the
polyester. These polyesters were pelletized in preparation for
coextrusion by feeding them into a 27 mm LEISTRITZ compounder with
a 40:1 length to diameter ratio at 240.degree. C. The pellets were
then dried at 43.degree. C. for 16 hours, and coextruded with a tie
layer consisting of a 70/30 polyether/polypropylene mix. The mass
ratio of polyester to tie layer is 3:1, and the melt temperature
was 238.degree. C. The two layers were coextruded through a 500 mm
wide die with a die gap of 1 mm. The distance between the die exit
and the nip between the chill roll and pressure roll was 140 mm. A
web consisting of a polypropylene laminate, tie layer, and paper
also passed through the nip and the extrudate was quenched with the
tie layer in contact with the polypropylene side.
An experiment was performed comparing the extrusion characteristics
of the branched and the unbranched polyester. The extruder rpms
were set so that the thickness at 240 m/min would be 4 .mu.m. The
paper conveyance speed was gradually increased to determine the
coating characteristics as a function of speed. As the speed with
the unbranched coextrusion increased, draw resonance also
increased. At speeds of about 210 m/min, the draw resonance was so
severe that the melt curtain repeatedly broke, showing that this
was an unrunnable condition. At 200 m/min, the draw resonance was
30%, where the draw resonance is defined as the (maximum
width-minimum width)/maximum width.
Similarly, the same experiment was performed with the polyester
that had 2% branching agent. This material conveyed easily at 240
m/min, with no draw resonance. This product was printed in a
thermal printer with acceptable color production.
EXAMPLE 3
The following formulation for a dye-receiving layer according to
the present invention was made:
70.07% polyester with 2% branching agent
12.78% LEXAN 151 bisphenol A polycarbonate
5.13% Dioctyl sebacate
12.0% MB50-315 silicone
0.02% phosphorous acid
This material was melt compounded using conditions similar to those
described above, but in a 50 mm compounder. The material was
pelletized, then dried at 43.degree. C. for 12 hours, and
coextruded with a 3:1 ratio of tie layer, consisting of 70%
PELESTAT 300 polyether and 30% polypropylene. The extrusion
temperature was 238.degree. C., the die gap was 0.75 mm, and the
width was about 1270 mm. The distance between the die exit and the
nip formed by the chill roll and the pressure roll is about 190 mm.
This material was extruded onto the same substrate as described in
example 2, and a line speed of 240 m/min was achieved with no draw
resonance.
This material was printed in a thermal printer using the following
dye donor and the color and quality were excellent.
Dye Donor:
A dye donor element of sequential areas of cyan, magenta and yellow
dye was prepared by coating the following layers in order on a 6
.mu.m poly(ethylene terephthalate) support:
(1) Subbing layer of TYZOR TBT (titanium tetra-n-butoxide) (DuPont
Co.) (0.12 g/m.sup.2) from a n-propyl acetate and 1-butanol solvent
mixture.
(2) Dye-layer containing Cyan Dye 1 (0.42 g/m2) illustrated below,
a mixture of Magenta Dye 1 (0.11 g/m2) and Magenta Dye 2 (0.12
g/m2) illustrated below, or Yellow Dye 1 illustrated below (0.20
g/m.sup.2) and S-363N1 (a micronized blend of polyethylene,
polypropylene and oxidized polyethylene particles) (Shamrock
Technologies, Inc.) (0.02 g/m.sup.2) in a cellulose acetate
propionate binder (2.5% acetyl, 45% propionyl) (0.15-0.70
g/m.sup.2) from a toluene, methanol, and cyclopentanone solvent
mixture.
On the reverse side of the support was coated:
(1) Subbing layer of TYZOR TBT (0.12 g/m.sup.2) from a n-propyl
acetate and 1-butanol solvent mixture.
(2) Slipping layer of Emralon 329 (a dry film lubricant of
poly(tetrafluoroethylene) particles in a cellulose nitrate resin
binder) (Acheson Colloids Corp.) (0.54 g/m.sup.2), p-toluene
sulfonic acid (0.0001 g/m.sup.2), BYK-320 (copolymer of a
polyalkylene oxide and a methyl alkylsiloxane) (BYK Chemie, USA)
(0.006 g/m.sup.2), and Shamrock Technologies Inc. S-232 (micronized
blend of polyethylene and camauba wax particles) (0.02 g/m2),
coated from a n-propyl acetate, toluene, isopropyl alcohol and
n-butyl alcohol solvent mixture. ##STR20##
The dye side of the dye-donor element approximately 10 cm.times.13
cm in area was placed in contact with the polymeric receiving layer
side of the dye-receiver element of the same area. The assemblage
was fastened to the top of a motor-driven 56 mm diameter rubber
roller and a TDK Thermal Head L-231, thermostated at 22.degree. C.,
was pressed with a spring at a force of 36 Newtons (3.2 kg) against
the dye-donor element side of the assemblage pushing it against the
rubber roller.
The imaging electronics were activated and the assemblage was drawn
between the printing head and roller at 7.0 mm/sec. Coincidentally,
the resistive elements in the thermal print head were pulsed in a
determined pattern for 29 .mu.sec/pulse at 129 .mu.sec intervals
during the 33 msec/dot printing time to create an image. When
desired, a stepped density image was generated by incrementally
increasing the number of pulses/dot from 0 to 255. The voltage
supplied to the print head was approximately 24.5 volts, resulting
in an instantaneous peak power of 1.27 watts/dot and a maximum
total energy of 9.39 mJoules/dot.
Individual cyan, magenta and yellow images were obtained by
printing from three dye-donor patches. When properly registered a
full color image was formed. The Status A red, green, and blue
reflection density of the stepped density image at maximum density,
Dmax, were read and recorded.
The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *